2,256 research outputs found
Wang-Landau sampling in three-dimensional polymers
Monte Carlo simulations using Wang-Landau sampling are performed to study
three-dimensional chains of homopolymers on a lattice. We confirm the accuracy
of the method by calculating the thermodynamic properties of this system. Our
results are in good agreement with those obtained using Metropolis importance
sampling. This algorithm enables one to accurately simulate the usually hardly
accessible low-temperature regions since it determines the density of states in
a single simulation.Comment: 5 pages, 9 figures arch-ive/Brazilian Journal of Physic
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On the relation between Transversal and Longitudinal Scaling in Cities
Given that a group of cities follows a scaling law connecting urban population with socio-economic or infrastructural metrics (transversal scaling), should we expect that each city would follow the same behavior over time (longitudinal scaling)? This assumption has important policy implications, although rigorous empirical tests have been so far hindered by the lack of suitable data. Here, we advance the debate by looking into the temporal evolution of the scaling laws for 5507 municipalities in Brazil. We focus on the relationship between population size and two urban variables, GDP and water network length, analyzing the time evolution of the system of cities as well as their individual trajectory. We find that longitudinal (individual) scaling exponents are city-specific, but they are distributed around an average value that approaches to the transversal scaling exponent when the data are decomposed to eliminate external factors, and when we only consider cities with a sufficiently large growth rate. Such results give support to the idea that the longitudinal dynamics is a micro-scaling version of the transversal dynamics of the entire urban system. Finally, we propose a mathematical framework that connects the microscopic level to global behavior, and, in all analyzed cases, we find good agreement between theoretical prediction and empirical evidence
Model to predict shrinkage and ejection forces of injection moulded tubular parts of short glass fiber reinforced thermoplastics
This work presents a model to predict shrinkage and ejection forces for glass fiber
reinforced thermoplastics of tubular geometry. This mathematical model was based in
Jansen’s Model to predict shrinkage and residual stresses in fiber reinforced injection molded
products and Pontes’s Model to predict ejection forces for tubular parts of pure PP. The
model used the modified classical laminate theory applied to injection moulding and it uses
the fiber orientation state, temperature and pressure field as input and which predicts the
shrinkage and ejection forces. The fiber orientation state was determined experimentally and
the temperature and pressure fields were obtained by MOLDFLOW simulations. The model to
predict ejection forces considers also the fiber orientation state, friction coefficient between
steel and polymer, elastic modulus of polymer, both in the ejection temperature and
diametrical shrinkage. The model is validated by experimental results
Assessment of the shrinkage and ejection forces of reinforced polypropylene based on nanoclays and short glass fibre
In this study the influence of nanoclay and glass fibre in the shrinkage and ejection forces
in polypropylene matrix in tubular parts moulded by injection moulding were analysed. An
instrumented mould was used to measure the part surface temperature and ejection forces in tubular
parts. The materials used were a polypropylene homopolymer Domolen 1100L nanoclay for
polyolefin nanocomposites P-802 Nanomax in percentages of 2%, 6% and 10% and a
polypropylene homopolymer with content of 10% of glass fibre Domolen P1-013-V10-N and 30%
of glass fibre Domolen P1-102-V30-N with 2% of nanoclay. The shrinkage and ejection forces
were analysed. The results show that the incorporation of nanoclays decreases the shrinkage and
ejection forces whereas glass fibre decreases the shrinkage and increase ejection forces due to the
increase of the elastic modulus. The nanoclays decrease the ejection force when compared with
glass fibre and pure PP. The effects of nanoclays are less pronounced than those of glass fibre.
The effect of the mould temperatures on the ejection forces in the mouldings produced with the
mentioned materials were also analysed. The ejection force decreases with the increase of the
temperature of the mould
Complete high-precision entropic sampling
Monte Carlo simulations using entropic sampling to estimate the number of
configurations of a given energy are a valuable alternative to traditional
methods. We introduce {\it tomographic} entropic sampling, a scheme which uses
multiple studies, starting from different regions of configuration space, to
yield precise estimates of the number of configurations over the {\it full
range} of energies, {\it without} dividing the latter into subsets or windows.
Applied to the Ising model on the square lattice, the method yields the
critical temperature to an accuracy of about 0.01%, and critical exponents to
1% or better. Predictions for systems sizes L=10 - 160, for the temperature of
the specific heat maximum, and of the specific heat at the critical
temperature, are in very close agreement with exact results. For the Ising
model on the simple cubic lattice the critical temperature is given to within
0.003% of the best available estimate; the exponent ratios and
are given to within about 0.4% and 1%, respectively, of the
literature values. In both two and three dimensions, results for the {\it
antiferromagnetic} critical point are fully consistent with those of the
ferromagnetic transition. Application to the lattice gas with nearest-neighbor
exclusion on the square lattice again yields the critical chemical potential
and exponent ratios and to good precision.Comment: For a version with figures go to
http://www.fisica.ufmg.br/~dickman/transfers/preprints/entsamp2.pd
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